Vacuum IG units are known in the art. For example, see U.S. Pat. Nos. 5,664,395 and 5,657,607, the disclosures of which are both hereby incorporated herein by reference.
Prior art FIGS. 1-2 illustrate a conventional vacuum IG unit. IG unit 1 includes two spaced apart sheets of glass 2 and 3 which enclose a vacuumed or low pressure space therebetween. Glass sheets 2 and 3 are interconnected by peripheral seal of fused solder 4 and an array of support pillars 5.
Pump out tube 8 is hermetically sealed by fused solder glass 9 to an aperture or hole 10 which passes from an interior surface of glass sheet 2 to the bottom of recess 11 in the exterior face of sheet 2. Recess 11 allows pump out tube 8 to be melted and sealed leaving a stub which does not protrude beyond the plane of the exterior face of sheet 2. When sheets 2, 3 and peripheral/edge seal 4 are in place, prior to the tube being sealed, a vacuum is attached to pump out tube 8 so that the interior cavity between sheets 2 and 3 can be vacuumed out to create a low pressure area. Chemical getter 12 may optionally be included within a machined recess 13 in one of the glass sheets of the IG unit to counteract any rise in pressure due to out-gassing.
FIG. 3 is a side cross sectional view of another conventional vacuum IG unit, including support pillars 5 disposed between opposing glass substrates 2 and 3. The periphery of the unit is hermetically sealed by edge seal 4 of fused solder glass.
Pillars are in contact with opposing glass substrates 2 and 3, as shown in FIGS. 1-3. However, the heating of one substrate to a temperature greater than the other may cause pillar(s) to scratch and/or crack one of the glass substrates. For example, when substrate 3 is heated (e.g. a hot object is placed on substrate 3 or it is exposed to direct sunlight), the heated substrate 3 may expand as a function of temperature and the other substrate 2 (which is not heated as much) may not expand at all or not to the same degree. This results in the substrate(s) sliding or moving relative to one another when one expands more than the other. Such relative movement or sliding may cause pillar(s) 5 to dig into, scratch, or crack one or both of glass substrates 2, 3. This weakens the glass and the vacuum IG unit as a whole, and may also create aesthetic problems.
U.S. Pat. No. 5,124,185, incorporated herein by reference, discloses an IG unit including support pillars located between opposing substrates. Each pillar is adhesively secured to one of the substrates, with the opposite side of each pillar having a Teflon (trademark) coating thereon. Unfortunately, because each pillar is secured to one of the substrates, relative movement of the glass substrates may cause pillar(s) to dig into, scratch, and/or crack a glass substrate. The pillars cannot slide relative to both substrates.
In view of the above, there exists a need in the art for pillars less likely to scratch substrate(s) of a vacuum IG unit when the opposing substrates are subjected to relative movement, and/or a need for pillars that will minimize or reduce the severity of scratching and/or cracking of vacuum IG glass substrates.
It is a purpose of this invention to fulfill any or all of the above described needs in the art, as well as other needs which will become apparent to the skilled artisan from the following detailed description of this invention.